1. Field of the Invention
The present invention relates to an electric discharge machine, and more particularly to a method and apparatus for controlling an electric discharge machine in which the ratio of occurrence of abnormal electric discharge occurring from the interpolar insulation malfunction is detected. The optimum value for the interpolar status during the interruption of the electric discharge is automatically adjusted corresponding to the interpolar condition, while a plurality of combinations of the electrical processing conditions by the input of process characteristics, such as process velocity and degree of roughness of the finishing surface, such as the maximum value of the electric discharge current and the time of interruption of the electric discharge, corresponding to those process characteristics are displayed, in order, on a display apparatus.
2. Description of the Related Art
It is well known that in order to be able to increase the efficiency of the electric discharge process the time of interruption of electric discharge may be reduced. However, if this interruption time is reduced excessively, a fine powder of processed metal and so on removed in the melted form is not adequately discharged from the working gap. Then the insulating conditions of the working gap do not adequately recover before a pulse voltage is applied. Abnormal discharge, such as arcing, is produced, so that the accuracy and efficiency of the machining of the workpiece is reduced. Accordingly, the time of interruption of electric discharge must be suitably controlled to match the interpolar insulation conditions.
However, the speed of restoration of these insulation conditions is not uniform, but is, for example, effected by the flow conditions of the dielectric fluid and the electric discharge time, etc. Accordingly, it is difficult for the operator to set the time of interruption of the electric discharge to match the conditions existing each time this occurs.
In addition, it is necessary to set the processing conditions, such as appropriate electrodes, polarity, maximum value of electric discharge current, time of interruption of electric discharge, etc., according to the processing characteristics, such as the material of the workpiece, the roughness of the finished surface, process speed, etc. Because there are a great number of combinations of these processing conditions, it becomes an extremely complex and difficult problem for the operator to set these conditions individually.
Accordingly, with conventional equipment, the method is used by which many matched process characteristics and process characteristics and process conditions are stored in the memory of the control equipment, and the operator selects the appropriate conditions to conform to the desired process characteristics from among the matching conditions displayed on the display equipment, and sets these conditions, in the control device. In such a method, a plurality of process conditions are generally required to satisfy a single process characteristic. For example, in the case where among the process characteristics, only the finished surface roughness is important, and other characteristics are not looked upon as being particularly important, the number or freedom of process conditions which can be selected becomes fairly large. In other words, the smaller the number of required process characteristics is, the more the freedom of the process conditions. Accordingly, it is not desirable to set process characteristics and process conditions one against one when the freedom of process characteristics is large because the operator's selection is unduly limited.